Maven is still very much alive, but still suffers from a serious lack of understanding. It can appear very daunting at first, and going through the documentation does not do much to make that feeling go away. Here are some tips that I would have loved being told when I first started using Maven.

A Quick Introduction

I won’t go into too much details (you probably already know about Maven’s dependency management) here, but will quickly describe what I think is important to know before using Maven. Maven helps you build a project. The way it does that is through the build lifecycle and the plugins.

The lifecycle is made of phases that you can call explicitly on the command line, for example:

mvn package

package is a phase part of the default build lifecycle, like compile or deploy. All the phases of the default lifecycle can be found in the reference. At each phase, Maven calls a goal in a plugin that does something for you. For example, the maven-compiler-plugin has a compile goal that compiles your java code during the compile phase of the lifecycle. You can also explicitly call a plugin on the command line, like:

mvn clean:clean

which calls the clean goal on the maven-clean-plugin. By default this goal is bound to the clean phase, so you can call it by executing mvn clean. You can call any plugin by using its group id, its artifact id, its version and the goal you want to execute, e.g.:

Here we are attaching the mirah compile goal to the compile phase of the lifecycle. When Maven executes the compile phase, it will the compile the Mirah code for us.

That’s pretty much the most important stuff you need to understand to get going with Maven: build lifecycle and plugin goals. Once you understand this, the hardest part is to find the plugin that does what you want, and going through its documentation to see how to configure it.

Here are the Tips!

In no particular order.

How to find a plugin goals?

Use the help goal for that plugin, for example:

mvn dependency:help
You can also use the @help@ plugin:

mvn help:describe -Dplugin=de.saumya.mojo:rake-maven-plugin:1.0.0-rc3

How to get completion on the command line?

Check out this project in GitHub. After a while it becomes impossible to do without.

How to find a project dependencies?

To list all the dependencies of the project:

mvn dependency:list

To display a tree of the transitive dependencies of the project:

mvn dependency:tree

How to download dependencies’ sources?

mvn dependency:sources

How to copy dependencies locally?

Use:

mvn dependency:copy-dependencies -DoutputDirectory=/tmp

This copies all the dependencies into the /tmp folder. To do this automatically during the package phase, add the plugin to your pom, as follows:

How to remove the dependencies from the local repo?

By default, purge-local-repository will then re-resolve your dependencies. If you don’t want that behaviour, add -DreResolve=false on the command line.

This is particularly handy when, for some reason, Maven is choking on a dependency that was temporarily unavailable, stubbornly refusing to download it again.

How to find a dependency?

To find the coordinates of a dependency, you can use http://mvnrepository.com. You can also use a ruby gem I have written, called mvnizer. Once installed (gem install mvnizer), you can easily search for existing artefacts:

When it comes to interacting between Maven and Ruby, the TorqueBox JRuby Maven plugins are the best solutions. Mostly maintained by Christian (who has also done a lot of work converting JRuby to Maven), they work quite well, albeit lacking in documentation.

As part of these plugins, the rake-maven-plugin allows you to call Rake tasks in a project, which can be useful if the build tool of your comapny is based on Java, but your project is Ruby-based (and you don’t want to use JRuby). To illustrate its use, we’ll use a very straightforward Rakefile:

task :do_that_thing do
puts " *** RAKE RUNNING ***"
end

It has a unique task, do_that_thing, that we’ll call from Maven. In the pom, you need to add the rake-maven-plugin:

The goal we are calling on the Rake plugin is rake, and the name of the Rake task is passed in args. As we are using Rake, we need to define a gem dependency to rake. To do so, you first need to add the rubygems Maven repo provided by TorqueBox:

To illustrate the use of Java annotations with JRuby code, I have put together a little Spring MVC example. This is quite straightforward, especially if you are familiar with Spring MVC already.

The Controller in JRuby

The “heart” of the app is the Spring MVC controller which must be annotated with the Controller annotation, and its request path defined with the RequestMapping annotation:

We also put the class in the com.weblogism.myapp package, we’ll see why in a second.

Spring Configuration

The Spring MVC configuration is pretty much “standard”:

It defines the component-scan tag that will look for all the classes annotated with Controller in the com.weblogism.myapp; you now see why we used java_package for our controller.

Compiling

The compiling and packaging is done by Maven. Again, nothing really extraordinary in the pom.xml. The only unconventional feature is the use of the jruby-maven-plugin to compile our JRuby class into a Java class:

It generates its output into target/generate-sources/jruby, and compiles out class into target/classes, like any other Java class. The output of the build is a war file that can be deployed in a Java EE container.

Running

To see our amazing app in action, run Jetty:

mvn jetty:run

Once Jetty is up, you can access the app at http://localhost:8080/welcome.html

I have been struggling with a weird cucumber issue today, as it took me some time to figure out what was going on, I thought I’d share this in case somebody is going down the same path.

It started when I decided to upgrade my cucumber-jvm example to the latest version (1.1.3). Quickly after upgrading, I hit that error:

java.lang.ArrayIndexOutOfBoundsException: -1
at java.util.ArrayList.get(ArrayList.java:324)
at gherkin.formatter.JSONFormatter.getFeatureElement(JSONFormatter.java:199)
at gherkin.formatter.JSONFormatter.addHook(JSONFormatter.java:156)
at gherkin.formatter.JSONFormatter.before(JSONFormatter.java:147)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)

So I rebuilt gherkin locally, thinking it would solve all my problems, and I was still the exact same error, at the same line number. After changing version, deleting the jar from the Maven repository, I was still getting the same error, so it was clear that the class was being pulled from somewhere else.

It turns out the jar was being pulled from cucumber-picocontainer, which uses shade to create an über-jar with its dependencies, including gherkin. How did I figure that out? Using this piece of code:

Passing your own properties

If you need to define your own properties and want to pass them either from the command line with -D=, or from the <properties> tag, and want to be able to retrieve these system properties from your step definitions, you must add an entry in the systemPropertyVariables tag when configuring failsafe. For example, say you want to have a ui.language property, add that property to the properties tag:

This will cause failsafe to pass on this property to the forked JVM running the tests. You can then override the “default” property either in a profile, or on the command line:

mvn install -Dui.language=EN

Note that this will work properly when cucumber-jvm 1.0.15 is released; until then you need to re-define the glue and path to features if you override cucumber.options, as setting that system properties clears all options set by the Cucumber.Options annotation.

This post will show how to use cucumber-jvm and Maven to run integration tests with Selenium on a regular webapp; as you’ll see, this is more of a Maven exercise than a cucumber-jvm one, as Cucumber tests are simply executed as JUnit tests. It can be a bit tricky as it requires a bit of Maven build lifecycle knowledge1, but once you get the idea, it all makes perfect sense.

The first thing we want to do is to segregate the integration tests from the unit tests. The reason for this is that it makes it easier to locate them, but also it allows you to run them separately: this is especially important if you want run the integration tests as part of your CI build. I personally prefer to have my integration tests under src/it/java, and suffixed with IT, so to do this, we first create a new profile and add the maven-failsafe-plugin:

The profile will be helpful to separate the integration tests execution if you want to run only in certain situations; it can also be used to define property values specifically for integration tests.

We then create the src/it/java and src/it/resources folders: src/it/resources will contain the feature files, whereas src/it/java will contain the step definitions and the JUnit test cases to be executed. We also need to add the new source folders to
the build with the build-helper-maven-plugin:

The JUnit test case is very simple:

It actually is empty: it cannot contain any method. It uses the Cucumber JUnit runner. The Cucumber.Options can be used to specify the format of the report created during the test, the feature files to execute, or the tags to run.

Next, the feature file is here somewhat trivial:

Finally, here are the step definitions:

As you can see, we are using the Selenium client in this step definition. We therefore need to add the dependencies to selenium (along with the cucumber-jvm ones) in our profile:

We also need to start the selenium server before the tests begin:

This plugin defines here two executions: start-selenium-server, which is executed before the integration tests during the phase called pre-integration-test, and calls the start goal, and stop-selenium-server called after the integration tests, during the post-integration-test phase, and that calls the stop goal of that plugin (for a reminder of the different phases of the build lifecycle, see the reference).

Finally, we configure the Jetty maven plugin to start and deploy the war we want to test:

Similarly to the selenium plugin, we start the Jetty server pre-integration-test (by running the run goal, and stop it post-integration-test with the stop goal.

We can now execute the tests by running:

mvn clean verify -Pintegration-tests

The -P flag indicates that Maven must activate the integration-tests profile; as the plugins and dependencies are defined in that profile, the integration tests will only be executed if you activate that profile.

Summary

All the required “services” (Jetty, Selenium) are started during the pre-integration-test phase, and then stopped during the post-integration-test phase. The cucumber integration tests stored in src/it/java are executed during the integration-test phase by running the JUnit tests that use Cucumber.class as a runner.

To run the integration tests:

Create a new profile,

Add src/it/java as a test source folder,

Create your feature file,

Implement the step definitions,

Add the failsafe plugin,

Add the selenium server plugin,

Add the jetty plugin.

Hope this helps!

1 Once you’ve understood the build lifecycle, you understand Maven, so most definitely a knowledge worth having!

Probably not what Mr. Yegge had in mind, but still inspiring all the same: analysing how many SNPs are in common between different populations using ruby and mongodb.

SNP (snip) stands for single-nucleotide polymorphism it is a variation of a single base pair amongst individuals of a species. SNPs can occur in coding and non-coding sequences, or between genes in the genome and can be used to identity genotypes.